The present invention relates to pyrazolo[3,4-d]pyrimidine derivatives, compositions and medicaments containing the same, as well as processes for the preparation and use of such compounds, compositions and medicaments. Such pyrazolo[3,4-d]pyrimidine derivatives are useful in the treatment of diseases associated with inappropriate angiogenesis.
The process of angiogenesis is the development of new blood vessels, generally capillaries, from pre-existing vasculature. Angiogenesis is defined as involving: (i) activation of endothelial cells; (ii) increased vascular permeability; (iii) subsequent dissolution of the basement membrane and extravisation of plasma components leading to formation of a provisional fibrin gel extracellular matrix; (iv) proliferation and mobilization of endothelial cells; (v) reorganization of mobilized endothelial cells to form functional capillaries; (vi) capillary loop formation; and (vii) deposition of basement membrane and recruitment of perivascular cells to newly formed vessels. Normal angiogenesis is activated during tissue growth, from embryonic development through maturity, and then enters a period of relative quiescence during adulthood. Normal angiogenesis is also activated during wound healing, and at certain stages of the female reproductive cycle. Inappropriate angiogenesis has been associated with several disease states including various retinopathies; ischemic disease; atherosclerosis; chronic inflammatory disorders; and cancer. The role of angiogenesis in disease states is discussed, for instance, in Fan et al., Trends in Pharmacol. Sci. 16: 54–66; Shawver et al., DDT Vol. 2, No. 2 February 1997; Folkmann, 1995, Nature Medicine 1: 27–31; Colville-Nash and Scott, Ann. Rheum. Dis., 51, 919, 1992; Brooks et al., Cell, 79, 1157, 1994; Kahlon et al., Can. J. Cardiol. 8, 60, 1992; Folkman, Cancer Biol, 3, 65, 1992; Denekamp, Br. J. Rad. 66, 181, 1993; Fidler and Ellis, Cell, 79, 185, 1994; O'Reilly et al., Cell, 79, 315, 1994; Ingber et al., Nature, 348, 555, 1990; Friedlander et al., Science, 270, 1500, 1995; Peacock et al., J. Exp. Med. 175, 1135, 1992; Peacock et al., Cell. Immun. 160, 178, 1995; and Taraboletti et al., J. Natl. Cancer Inst. 87, 293, 1995.
In cancer the growth of solid tumors has been shown to be angiogenesis dependent. (See Folkmann, J., J. Nat'l. Cancer Inst., 1990, 82, 4–6.) Consequently, the targeting of pro-angiogenic pathways is a strategy being widely pursued in order to provide new therapeutics in these areas of great, unmet medical need. The role of tyrosine kinases involved in angiogenesis and in the vascularization of solid tumors has drawn interest. Until recently most interest in this area has focused on growth factors such as vascular endothelial growth factor (VEGF) and its receptors termed vascular endothelial growth factor receptor(s) (VEGFR). VEGF, a polypeptide, is mitogenic for endothelial cells in vitro and stimulates angiogenic responses in vivo. VEGF has also been linked to inappropriate angiogenesis (Pinedo, H. M. et al. The Oncologist, Vol. 5, No. 90001, 1–2, April 2000). VEGFR(s) are protein tyrosine kinases (PTKs). PTKs catalyze the phosphorylation of specific tyrosyl residues in proteins involved in the regulation of cell growth and differentiation. (A. F. Wilks, Progress in Growth Factor Research, 1990, 2, 97–111; S. A. Courtneidge, Dev. Supp. 1, 1993, 57–64; J. A. Cooper, Semin. Cell Biol., 1994, 5(6), 377–387; R. F. Paulson, Semin. Immunol., 1995, 7(4), 267–277; A. C. Chan, Curr. Opin. Immunol., 1996, 8(3), 394–401).
Three PTK receptors for VEGF have been identified: VEGFR-1 (Flt-1); VEGFR-2 (Flk-1 or KDR) and VEGFR-3 (Flt-4). These receptors are involved in angiogenesis and participate in signal transduction (Mustonen, T. et al. J. Cell Biol. 1995, 129: 895–898). Of particular interest is VEGFR-2, which is a transmembrane receptor PTK expressed primarily in endothelial cells. Activation of VEGFR-2 by VEGF is a critical step in the signal transduction pathway that initiates tumor angiogenesis. VEGF expression may be constitutive to tumor cells and can also be upregulated in response to certain stimuli. One such stimuli is hypoxia, where VEGF expression is upregulated in both tumor and associated host tissues. The VEGF ligand activates VEGFR-2 by binding with its extracellular VEGF binding site. This leads to receptor dimerization of VEGFRs and autophosphorylation of tyrosine residues at the intracellular kinase domain of VEGFR-2. The kinase domain operates to transfer a phosphate from ATP to the tyrosine residues, thus providing binding sites for signaling proteins downstream of VEGFR-2 leading ultimately to initiation of angiogenesis (McMahon, G., The Oncologist, Vol. 5, No. 90001, 3–10, April 2000).
Angiopoieten 1 (Ang1), a ligand for the endothelium-specific receptor tyrosine kinase TIE-2 is a novel angiogenic factor (Davis et al., Cell, 1996, 87: 1161–1169; Partanen et al., Mol. Cell Biol., 12: 1698–1707 (1992); U.S. Pat. Nos. 5,521,073; 5,879,672; 5,877,020; and 6,030,831). The acronym TIE represents “tyrosine kinase containing Ig and EGF homology domains”. TIE is used to identify a class of receptor tyrosine kinases, which are exclusively expressed in vascular endothelial cells and early hemopoietic cells. Typically, TIE receptor kinases are characterized by the presence of an EGF-like domain and an immunoglobulin (IG) like domain, which consists of extracellular folding units, stabilized by intra-chain disulfide bonds (Partanen et al., Curr. Topics Microbiol. Immunol., 1999, 237: 159–172). Unlike VEGF, which functions during the early stages of vascular development, Ang1 and its receptor TIE-2 function in the later stages of vascular development, i.e., during vascular remodeling (remodeling refers to formation of a vascular lumen) and maturation (Yancopoulos et al., Cell, 1998, 93: 661–664; Peters, K. G., Circ. Res., 1998, 83(3): 342–3; Suri et al., Cell 87, 1996: 1171–1180).
Consequently, inhibition of TIE-2 would be expected to serve to disrupt remodeling and maturation of new vasculature initiated by angiogenesis thereby disrupting the angiogenic process. Furthermore, inhibition at the kinase domain binding site of VEGFR-2 would block phosphorylation of tyrosine residues and serve to disrupt initiation of angiogenesis. Presumably then, inhibition of TIE-2 and/or VEGFR-2 should prevent tumor angiogenesis and serve to retard or eradicate tumor growth. Accordingly, a treatment for cancer or other disorder associated with inappropriate angiogenesis could be provided.
The present inventors have discovered novel pyrazolo[3,4-d]pyrimidine compounds, which are inhibitors of one or more of TIE-2 kinase activity, VEGFR-2 kinase activity, and VEGFR-3 kinase activity, e.g., one or both TIE-2 kinase and VEGFR-2 kinase activity. Such pyrazolo[3,4-d] pyrimidine derivatives are useful in the treatment of disorders, mediated by at least one of inappropriate TIE-2 kinase, VEGFR-2 kinase, and VEGFR-3 activity (which may include cancer and/or diseases afflicting mammals which is characterized by cellular proliferation in the area of disorders associated with neo-vascularization and/or vascular permeability), and/or disorders characterized by inappropriate angiogenesis; and/or for treating cancer and/or a disease afflicting afflicting mammals which is characterized by cellular proliferation in the area of disorders associated with neo-vascularization and/or vascular permeability.